Sustainable microbial melanin pigment production from citrus peel side streams

Overview

This solution offers a sustainable biotechnological route to microbial melanin pigment by using side stream biomass from pectin production as the fermentation substrate. Streptomyces strains are cultivated on this lignocellulosic residue with minimal pre-treatment, converting an industrial by-product into a high-value biochemical. The resulting melanin is an extracellular polymer pigment with strong thermal stability, antimicrobial activity, antioxidant and free radical scavenging capacity, metal chelation, and broad UV-visible absorption. These properties make it attractive for cosmetic formulations, bio-based polymer additives for bioplastics and food packaging, and food ingredient or supplement applications. The process aligns with circular bio-economy principles by reducing waste while producing a versatile, naturally derived pigment.

Technical specifications

Process design:

• Batch fermentation using Streptomyces strains on pectin side stream biomass
• Semi-defined liquid medium with minimal pre-treatment (water removal and sterilization)
• Operating conditions: 28 to 30 degrees Celsius, pH 6.0 to 7.0, 96 hour fermentation cycle
• Pigment recovery via simple precipitation followed by acidic washes

Yield benchmarks:

• Prior studies on Posidonia oceanica egagropili and Magnolia grandiflora leaves with S. roseochromogenes ATCC 13400 and S. nashvillensis DSM 40314 reached up to 9.2 grams per liter of pigment
• Comparable yields demonstrated with Citrus sinensis and Citrus bergamia peels

Characterization methods: UV-visible spectroscopy, NMR, FT-IR, elemental analysis, and EPR for structural confirmation; antimicrobial and antioxidant assays for biological property validation.

Technology readiness level

The approach is at laboratory validation stage. Shake-flask studies in 1-liter vessels are planned to optimize substrate loading, pH, temperature, and stirring conditions over six to eight months. The purified pigment will then be structurally characterized and biologically tested over an additional two to four months each, followed by scale-up to 15-liter fermentation over six to eight months. The full project is estimated at up to 24 months, with several activities running in parallel to accelerate development toward pilot demonstration.